Fuel cell system and method for operating a fuel cell

Abstract

In a fuel cell system having a gas generation system for providing hydrogen from a carbon- and hydrogen-containing medium for a fuel cell unit, means are provided for adjusting pressure in the gas generation system and/or mass flow through the fuel cell unit, upstream of the fuel cell unit. In a transition from a part-load range to a full-load range, the pressure can be at least briefly reduced, and in a transition from a full-load range to a part-load range, the pressure can be at least briefly increased.

What is claimed is:  
     
       1. Fuel cell system comprising: 
       a gas generation system for providing hydrogen from a carbon- and hydrogen-containing medium for a fuel cell unit; and  
       pressure regulating means for adjusting at least one of pressure in the gas generation system and mass flow through the fuel cell unit as a function of a load on the fuel cell unit, which pressure regulating means are disposed upstream of the fuel cell unit;  
       wherein said pressure is adjusted in such a manner that,  
       during a transition from a part-load range to a full-load range, the pressure is momentarily reduced; and  
       during a transition from a full-load range to a part-load range, the pressure can be momentarily increased.  
     
     
       2. The fuel cell system according to  claim 1 , wherein the pressure regulating means comprises a pressure-regulating valve upstream of the fuel cell unit. 
     
     
       3. The fuel cell system according to  claim 1 , wherein the pressure regulating means comprises a mass-flow-regulating valve upstream of the fuel cell unit and a pressure sensor for influencing the metering of fuel at a metering device. 
     
     
       4. A method for operating a fuel cell system comprising a gas generation system for providing hydrogen from a carbon- and hydrogen-containing medium for a fuel cell units and pressure regulating means for adjusting at least one of pressure in the gas generation system and mass flow through the fuel cell unit as a function of a load on the fuel cell unit, which pressure regulating means are disposed upstream of the fuel cell unit, said method comprising: 
       during a transition from a part-load range to a full-load range, reducing pressure in the gas generation system momentarily; and  
       during a transition from a full-load range to a part-load range, increasing said pressure momentarily.  
     
     
       5. The method according to  claim 4 , wherein fuel for the fuel cell unit is metered in a manner which varies as a function of a load on the fuel cell unit. 
     
     
       6. The method according to  claim 4 , wherein fuel for the fuel cell unit is metered at a hither level in a full-load range than in a part-load range. 
     
     
       7. The method according to  claim 4 , wherein pressure in the gas generation system is set to be higher in a part-load range than in a full-load range. 
     
     
       8. The method according to  claim 4 , wherein pressure in the gas generation system is kept substantially constant except during load-changes. 
     
     
       9. The method according to  claim 1 , wherein pressure in the gas generation system is regulated by means of a pressure regulation valve. 
     
     
       10. The method according to  claim 4 , wherein a mass flow of a fuel supply to the fuel cell unit is regulated. 
     
     
       11. Fuel cell system comprising: 
       a gas generation system for providing hydrogen from a carbon- and hydrogen-containing medium for a fuel cell unit; and  
       pressure regulating means for adjusting at least one of pressure in the gas generation system and mass flow through the fuel cell unit as a function of a load on the fuel cell unit, which pressure regulating means are disposed upstream of the fuel cell unit;  
       wherein said pressure is adjusted in such a manner that,  
       the pressure is reduced during the occurrence of a transition from operation of the fuel cell at a maximum load to operation at a partial load, and increased to its previous value upon completion of operation at a partial load;  
       the pressure is increased during the occurrence of a transition from operation of the fuel cell at a maximum load to operation at a partial load, and increased to its previous value upon completion of operation at a partial load.  
     
     
       12. A method for operating a fuel cell system comprising a gas generation system for providing hydrogen from a carbon- and hydrogen-containing medium for a fuel cell unit, and pressure regulating means for adjusting at least one of pressure in the gas generation system and mass flow through the fuel cell unit as a function of a load on the fuel cell unit, which pressure regulating means are disposed upstream of the fuel cell unit, said method comprising: 
       reducing the pressure during the occurrence of a transition from operation of the fuel cell at a maximum load to operation at a partial load, and decreasing to its previous value upon completion of operation at a partial load;  
       increasing the pressure during the occurrence of a transition from operation of the fuel cell at a maximum load to operation at a partial load, and decreasing to its previous value upon completion of operation at a partial load.